Volatile composition of the critically endangered plant Thymus webbianus Rouy from the Natural Park “Penyal d’Ifach” (Calp, Spain)

Thymus webbianus Rouy (Lamiaceae) is an endemic plant known from only two populations located in the Natural Park “Penyal d'Ifac” (Calp), and in the Natural Park of Serra Gelada (Benidorm-Alfàs del Pi) in Spain. At the Spanish state level, it has been listed as "Critically Endangered", and "Vulnerable" in the Valencian Region. Moreover, its taxonomic position remains unclear, and further research on this species is needed. Therefore, this work was aimed to characterize the chemical composition in volatiles from four subpopulations located in the Natural Park “Penyal d’Ifach” through HS-SPME-GC-MS. An overall of 53 compounds were identified in these samples. Three major compounds (representing more than 5 % in peak area) were identified in all samples: β-caryophyllene (S1= 9.23 ± 0.19, S2= 6.29 ± 0.20, S3= 11.25 ± 0.74, and S4= 11.26 ± 0.34), D-limonene, (S1=5.01 ± 0.21, S2= 7.95 ± 0.34, S3= 10.54 ± 1.17, and S4= 9.22 ± 0.51), and bicyclogermacrene (S1= 5.21 ± 0.19, S2= 7.24 ± 0.79, S3= 7.07 ± 0.4, and S4= 5.37 ± 0.43). The other compounds were presented in lower amounts, and/or in a more reduced number of samples. The richness in β-caryophyllene, D-limonene, and bicyclogermacrene might be used as a marker, to separate T. webbianus from T. vulgaris. Also, the lack of thymol (a widespread terpene within the genus Thymus) could be characteristic of T. webbianus. However, given the large amount of chemotypes described for T. vulgaris this idea has to be treated with caution, and further studies on the phytochemistry of T. webbianus (including samples from T. vulgaris in the nearby, as well as samples from the natural hybrid T. ×valentinus) should be performed in order to clarify whether the chemical profile may be useful for the taxonomical arrangement of the species, and to clarify its conservation status.